package pers.wk.utils;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.lang.management.ManagementFactory;
import java.lang.management.RuntimeMXBean;
import java.net.NetworkInterface;
import java.net.SocketException;
import java.util.Enumeration;

/**
 * desc: 雪花算法生成编号
 *
 * @author jerryxia
 * @date 2020-05-08
 **/
public class SnowFlake {

    private static final Logger logger = LoggerFactory.getLogger(SnowFlake.class);

    private final static long TWEPOCH = 12888349746579L;
    /**机器标识位数*/
    private final static long WORKER_ID_BITS = 5L;
    /**数据中心标识位数*/
    private final static long DATACENTER_ID_BITS = 5L;

    /** 毫秒内自增位数*/
    private final static long SEQUENCE_BITS = 12L;
    /** 机器ID偏左移12位*/
    private final static long WORKER_ID_SHIFT = SEQUENCE_BITS;
    /** 数据中心ID左移17位*/
    private final static long DATACENTER_ID_SHIFT = SEQUENCE_BITS + WORKER_ID_BITS;
    /** 时间毫秒左移22位*/
    private final static long TIMESTAMP_LEFT_SHIFT = SEQUENCE_BITS + WORKER_ID_BITS + DATACENTER_ID_BITS;
    /**sequence掩码，确保sequnce不会超出上限*/
    private final static long SEQUENCE_MASK = -1L ^ (-1L << SEQUENCE_BITS);
    /**上次时间戳*/
    private static long LAST_TIMESTAMP = -1L;
    /**序列*/
    private long sequence = 0L;
    /**服务器ID*/
    private long workerId = 1L;
    private static long workerMask = -1L ^ (-1L << WORKER_ID_BITS);
    /**进程编码*/
    private long processId = 1L;
    private static long processMask = -1L ^ (-1L << DATACENTER_ID_BITS);

    private static SnowFlake snowFlake = null;

    static{
        snowFlake = new SnowFlake();
    }
    public static synchronized String nextId(){
        return snowFlake.getNextId()+"";
    }

    private SnowFlake() {

        //获取机器编码
        this.workerId=this.getMachineNum();
        //获取进程编码
        RuntimeMXBean runtimeMXBean = ManagementFactory.getRuntimeMXBean();
        this.processId=Long.valueOf(runtimeMXBean.getName().split("@")[0]).longValue();

        //避免编码超出最大值
        this.workerId=workerId & workerMask;
        this.processId=processId & processMask;
    }

    public synchronized long getNextId() {
        //获取时间戳
        long timestamp = timeGen();
        //如果时间戳小于上次时间戳则报错
        if (timestamp < LAST_TIMESTAMP) {
            try {
                throw new Exception("Clock moved backwards.  Refusing to generate id for " + (LAST_TIMESTAMP - timestamp) + " milliseconds");
            } catch (Exception e) {
                logger.error("异常信息:",e);
            }
        }
        //如果时间戳与上次时间戳相同
        if (LAST_TIMESTAMP == timestamp) {
            // 当前毫秒内，则+1，与SEQUENCE_MASK确保sequence不会超出上限
            sequence = (sequence + 1) & SEQUENCE_MASK;
            if (sequence == 0) {
                // 当前毫秒内计数满了，则等待下一秒
                timestamp = tilNextMillis(LAST_TIMESTAMP);
            }
        } else {
            sequence = 0;
        }
        LAST_TIMESTAMP = timestamp;
        // ID偏移组合生成最终的ID，并返回ID
        long nextId = ((timestamp - TWEPOCH) << TIMESTAMP_LEFT_SHIFT) | (processId << DATACENTER_ID_SHIFT) | (workerId << WORKER_ID_SHIFT) | sequence;
        return nextId;
    }

    /**
     * 再次获取时间戳直到获取的时间戳与现有的不同
     * @param lastTimestamp
     * @return 下一个时间戳
     */
    private long tilNextMillis(final long lastTimestamp) {
        long timestamp = this.timeGen();
        while (timestamp <= LAST_TIMESTAMP) {
            timestamp = this.timeGen();
        }
        return timestamp;
    }

    private long timeGen() {
        return System.currentTimeMillis();
    }

    /**
     * 获取机器编码
     * @return
     */
    private long getMachineNum(){
        long machinePiece;
        StringBuilder sb = new StringBuilder();
        Enumeration<NetworkInterface> e = null;
        try {
            e = NetworkInterface.getNetworkInterfaces();
        } catch (SocketException e1) {
            e1.printStackTrace();
        }
        while (e.hasMoreElements()) {
            NetworkInterface ni = e.nextElement();
            sb.append(ni.toString());
        }
        machinePiece = sb.toString().hashCode();
        return machinePiece;
    }
}